Gravity varies...
23 Sep 2008 8:33:16 UTC
Topic 193944
(moderation:
Somewhere in Lyall Watsons excellent book Supernature, it is mentioned that there is somewhere in Europe where "the pebbles sre not anchored on the beach as firmly as they should be..."
Presumably he is referring to a local gravity anomaly?
Waiting for Godot & salvation :-)
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You'd think they'd have got it right by now
Gravity varies...
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On October 5 a Russian rocket Rokot should put in orbit from Plesetsk the European Space Agency GOCE satellite (Gravity field and steady Ocean Circulation Explorer) whose mission is to map the Earth gravity field with great accuracy.
Tullio
RE: RE: ... Presumably he
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Is that not already being done by GRACE?
GRACE gravity
Just as interesting is the 'lumpyness' of our moon...
Keep searchin',
Martin
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RE: RE: RE: ...
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GOCE will orbit at at lower altitude (260 km instead of 500 km of GRACE) and since there will be still an atmospheric drag at that height GOCE is provided with an electric thrust engine, powered by solar cells,to maintain it in altitude and it has also wings, so it resembles an airplane more than a satellite. It is red colored and the project engineers call it the "Ferrari of space". Hope all goes well.
Thanks for the info, going to
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Thanks for the info, going to be interesting to see the results. According to Grace the variation is no more than +/- 60 millionths of normal, didn't realise it was so small.
Waiting for Godot & salvation :-)
Why do doctors have to practice?
You'd think they'd have got it right by now
Ah, so this is the
)
Ah, so this is the terrestrial version of 'mass-cons' ( mass concentrations ) that were discovered with the moon missions. With Apollo there was no air so the speed ups and slow downs ( compared to the assumption of a uniform density sphere ) could be sensed right down to surface. Not a trivial issue if you want to do a spot of rendezvousing.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Here on Earth we have the
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Here on Earth we have the oceans, whose density varies with temperature. So GOCE should be useful in watching also oceanic circulation, as its acronym implies. Really a very interesting satellite, I hope it launches well. The launcher had some problems and the launch was delayed already.
Tullio
RE: Here on Earth we have
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Yes, the variation is likely quite complex. You'd hopefully get a quicker and more complete data set than surface traversals with gravitometers. I think a bit of that sort of thing was done with Magellan at Venus too ....
Cheers, Mike.
( edit ) At a glance it looks like they are effectively measuring the gravity field gradient over the scale of the difference in position between each of the satellites. With this set of differentials, you could integrate ( to within a constant offset ) to get the field value. Neat idea of swapping over the leading for the trailing satellite mid-mission - a clever 'control' in the experiment. Gosh there's some smart bunnies out there.
( edit ) Oh my goodness, they are modeling the geode to within about a centimeter with spherical harmonics out to order 160! Newton would delight in this - he did calculations based on the Earths oblate sphericity ( 'fatter' around the equator, 'flatter' at the poles ) which is of order 1!
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
You are talking about the
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You are talking about the twin GRACE satellites, I believe. GOCE ha still to launch and, with its lower orbit, should provide even better data. I foresee a big problem in data processing, the data output should be huge. Cloud computing, anyone? Cheers.
Tullio
RE: You are talking about
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Quite right. GOCE measures the gradient in three axes, with position provided by GPS and laser. A full blooded direct construction of a vector field.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
RE: RE: You are talking
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GOCE has just reached orbit.
Tullio